The Open Systems Interconnection Model
(OSI) is a conceptual model that characterizes and standardizes the internal
functions of a communication system by partitioning it into abstraction layers.
The OSI Model is a conceptual, seven-layered model of how networks work. It
tells us that how data is going through one computer to another computer, and
also it simplifies to troubleshoot the network issues.
A reference model to make sure products
of different vendors would work together.
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| OSI (Open Systems Interconnection) Model & its & Layer |
HISTORY
In the late 1970s, two projects began
independently, with the same goal: to define a unifying standard for the
architecture of networking systems. One was administered by the International
Organization for Standardization (ISO), while the other was undertaken by the
International Telegraph and Telephone Consultative Committee, or CCITT (the
abbreviation is from the French version of the name). These two international
standards bodies each developed a document that defined similar networking
models.
In 1983, these two documents were
merged together to form a standard called The Basic Reference Model for Open
Systems Interconnection. That's a mouthful, so the standard is usually referred
to as the Open Systems Interconnection Reference Model, the OSI Reference
Model, or even just the OSI Model. It was published in 1984 by both the ISO, as
standard ISO 7498, and the renamed CCITT (now called the Telecommunications
Standardization Sector of the International Telecommunication Union or ITU-T)
as standard X.200.
The concept of a seven-layer model
was provided by the work of Charles Bachman, Honeywell Information Services.
OSI Network Interconnection
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| OSI Network Interconnection |
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| Packet Discription |
OSI LAYER
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| Physical Layer |
- It defines the electrical and
physical specifications of the data connection. It defines the relationship
between a device and a physical transmission medium (e.g., a copper or fiber
optical cable). This includes the layout of pins, voltages, line impedance,
cable specifications, signal timing, hubs, repeaters, network adapters, host
bus adapters (HBA used in storage area networks) and more.
- It defines the protocol to establish
and terminate a connection between two directly connected nodes over a
communications medium.
- It may define the protocol for flow
control.
- It defines transmission mode i.e.
simplex, half & full duplex.
- It defines topology.
- It defines a protocol for the
provision of a (not necessarily reliable) connection between two directly
connected nodes, and the modulation or conversion between the representation of
digital data in user equipment and the corresponding signals transmitted over
the physical communications channel. This channel can involve physical cabling
(such as copper and optical fiber) or a wireless radio link.
- Telephone network modems- V.92
- IRDA physical layer
- USB physical layer
- EIA RS-232, EIA-422, EIA-423, RS-449,
RS-485
- Ethernet physical layer Including
10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 100BASE-T, 1000BASE-T,
1000BASE-SX and other varieties
- Varieties of 802.11 Wi-Fi physical
layers
- DSL
- ISDN
- T1 and other T-carrier links, and E1
and other E-carrier links
- SONET/SDH
- Optical Transport Network (OTN)
- GSM Um air interface physical layer
- Bluetooth physical layer
- ITU Recommendations: see ITU-T
- IEEE 1394 interface
- TransferJet physical layer
- Etherloop
- ARINC 818 Avionics Digital Video Bus
- G.hn/G.9960 physical layer
- CAN bus (controller area network)
physical layer
- Mobile Industry Processor Interface
physical layer
2. Data Link Layer
The Data-Link layer contains two sub
layers that are described in the IEEE-802 LAN standards:
Media Access Control (MAC) layer- Responsible for controlling how computers in the network gain access to data
and permission to transmit it.
Logical Link Control (LLC) layer- Control error checking and packet synchronization.
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| Data Link Layer |
- Link establishment and termination:
establishes and terminates the logical link between two nodes.
- Frame traffic control: tells the
transmitting node to "back-off" when no frame buffers are available.
- Frame sequencing: transmits/receives
frames sequentially.
- Frame acknowledgment:
provides/expects frame acknowledgments. Detects and recovers from errors that
occur in the physical layer by retransmitting non-acknowledged frames and
handling duplicate frame receipt.
- Frame delimiting: creates and
recognizes frame boundaries.
- Frame error checking: checks received
frames for integrity.
- Media access management: determines
when the node "has the right" to use the physical medium.
- ARCnet Attached
Resource Computer NETwork
- CDP Cisco Discovery Protocol
- DCAP Data Link Switching Client
Access Protocol
- Distributed Multi-Link Trunking
- Distributed Split Multi-Link Trunking
- Dynamic Trunking Protocol
- Econet
- Ethernet
- FDDI Fiber Distributed Data Interface
- Frame Relay
- ITU-T G.hn Data Link Layer
- HDLC High-Level Data Link Control
- IEEE 802.11 WiFi
- IEEE 802.16 WiMAX
- LACP Link Aggregation Control
Protocol
- LattisNet
- LocalTalk
- L2F Layer 2 Forwarding Protocol
- L2TP Layer 2 Tunneling Protocol
- LAPD Link Access Procedures on the D
channel
- LLDP Link Layer Discovery Protocol
- LLDP-MED Link Layer Discovery
Protocol - Media Endpoint Discovery
- PAgP - Cisco Systems proprietary link
aggregation protocol
- PPP Point-to-Point Protocol
- PPTP Point-to-Point Tunneling
Protocol
- Q.710 Simplified Message Transfer
Part
- Multi-link trunking Protocol
- RPR IEEE 802.17 Resilient Packet Ring
- SLIP Serial Line Internet Protocol
(obsolete)
- StarLAN
- STP Spanning Tree Protocol
- Split multi-link trunking Protocol
- Token ring a protocol developed by IBM;
the name can also be used to describe the token passing ring logical topology
that it popularized.
- VTP VLAN Trunking Protocol
- VLAN Virtual Local Area Network
3. Network Layer
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| Network Layer |
- Routing: routes frames among
networks.
- Subnet traffic control: routers
(network layer intermediate systems) can instruct a sending station to
"throttle back" its frame transmission when the router's buffer fills
up.
- Frame fragmentation: if it determines
that a downstream router's maximum transmission unit (MTU) size is less than
the frame size, a router can fragment a frame for transmission and re-assembly
at the destination station.
- Logical-physical address mapping:
translates logical addresses, or names, into physical addresses.
- Subnet usage accounting: has
accounting functions to keep track of frames forwarded by subnet intermediate
systems, to produce billing information.
- ARP Address Resolution Protocol
- RARP Reverse Address Resolution
Protocol
- ATM Asynchronous Transfer Mode
- Frame relay, a simplified version of
X.25
- IS-IS, Intermediate System -
Intermediate System (OSI)
- MPLS Multi-protocol label switching
- SPB Shortest Path Bridging
- X.25
- MTP Message Transfer Part
- NSP Network Service Part
- HIP Host Identity Protocol
- AppleTalk
- DECnet
- IPX/SPX
- Internet Protocol Suite
- Xerox Network Systems
- TCP/IP
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| Transport Layer |
- Message segmentation: accepts a
message from the (session) layer above it, splits the message into smaller
units (if not already small enough), and passes the smaller units down to the
network layer. The transport layer at the destination station reassembles the
message.
- Message acknowledgment: provides
reliable end-to-end message delivery with acknowledgments.
- Message traffic control: tells the
transmitting station to "back-off" when no message buffers are
available.
- Session multiplexing: multiplexes
several message streams, or sessions onto one logical link and keeps track of
which messages belong to which sessions (see session layer).
- AH Authentication Header over IP or
IPSec
- IL Originally developed as transport
layer for 9P
- SCTP Stream Control Transmission
Protocol
- Sinec H1 for telecontrol
- SPX Sequenced Packet Exchange
- TCP Transmission Control Protocol
- UDP User Datagram Protocol
- DCCP Datagram Congestion Control
Protocol
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| Session Layer |
- Session establishment, maintenance
and termination: allows two application processes on different machines to
establish, use and terminate a connection, called a session.
- Session support: performs the
functions that allow these processes to communicate over the network,
performing security, name recognition, logging, and so on.
- 9P Distributed file system protocol
developed originally as part of Plan 9
- NetBIOS, File Sharing and Name
Resolution protocol - the basis of file sharing with Windows.
- NetBEUI, NetBIOS Enhanced User
Interface
- NCP NetWare Core Protocol
- NFS Network File System
- SMB Server Message Block
- SOCKS "SOCKetS"
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| Presentation Layer |
- Character code translation: for
example, ASCII to EBCDIC.
- Data conversion: bit order, CR-CR/LF,
integer-floating point, and so on.
- Data compression: reduces the number
of bits that need to be transmitted on the network.
- Data encryption: encrypt data for
security purposes. For example, password encryption.
- TLS Transport Layer Security
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| Application Layer |
- Resource sharing and device redirection
- Remote file access
- Remote printer access
- Inter-process communication
- Network management
- Directory services
- Electronic messaging (such as mail)
- Network virtual terminals
- ADC, A peer-to-peer file sharing
protocol
- AFP, Apple Filing Protocol
- BACnet, Building Automation and
Control Network protocol
- BitTorrent, A peer-to-peer file
sharing protocol
- BGP Border Gateway Protocol
- BOOTP, Bootstrap Protoc;
- CAMEL, an SS7 protocol tool for the
home operator
- Diameter, an authentication,
authorization and accounting protocol
- DICOM includes a network protocol
definition
- DICT, Dictionary protocol
- DNS, Domain Name System
- DSM-CC Digital Storage Media Command
and Control
- DSNP, Distributed Social Networking
Protocol
- DHCP, Dynamic Host Configuration
Protocol
- ED2K, A peer-to-peer file sharing
protocol
- FTP, File Transfer Protocol
- Finger, which gives user profile information
- Gnutella, a peer-to-peer
file-swapping protocol
- Gopher, a hierarchical hyperlinkable
protocol
- HTTP, Hypertext Transfer Protocol
- HTTPS, Hypertext Transfer Protocol
Secure
- IMAP, Internet Message Access
Protocol
- IRC, Internet Relay Chat
- ISUP, ISDN User Part
- LDAP Lightweight Directory Access
Protocol
- MIME, Multipurpose Internet Mail
Extensions
- MSNP, Microsoft Notification Protocol
(used by Windows Live Messenger)
- MAP, Mobile Application Part
- Mosh, Mobile Shell
- NNTP, Network News Transfer Protocol
- NTP, Network Time Protocol
- NTCIP, National Transportation
Communications for Intelligent Transportation System Protocol
- POP3 Post Office Protocol Version 3
- RADIUS, an authentication,
authorization and accounting protocol
- RDP, Remote Desktop Protocol
- Rlogin, a UNIX remote login protocol
- rsync, a file transfer protocol for
backups, copying and mirroring
- RTP, Real-time Transport Protocol
- RTSP, Real-time Transport Streaming
Protocol
- SSH, Secure Shell
- SISNAPI, Siebel Internet Session
Network API
- SIP, Session Initiation Protocol, a
signaling protocol
- SMTP, Simple Mail Transfer Protocol
- SNMP, Simple Network Management
Protocol
- SOAP, Simple Object Access Protocol
- SMB, Microsoft Server Message Block
Protocol
- STUN, Session Traversal Utilities for
NAT
- TUP, Telephone User Part
- Telnet, a remote terminal access
protocol
- TCAP, Transaction Capabilities
Application Part
- TFTP, Trivial File Transfer Protocol,
a simple file transfer protocol
- WebDAV, Web Distributed Authoring and
Versioning
- XMPP, an instant-messaging protocol
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